It says same day boarding pass, does that have to be outbound or can you use it on an inbound flight as an arrivals Lounge?
answering my own question: I’m in the FRA T1B F lounge. They accepted my inbound boarding pass. I do have a connecting flight tomorrow on *A (not LH group though) so not sure if that made the difference.
I did did not have a departing flight in this terminal (came in via another Shengen country) so had to go through passport control, but they let me in with a stamp on my passport.